Nanoparticles are of great scientific interest as they can be utilized in many industrial or medical applications. Nanoparticles are typically sized between 1 to 100 nm.
In particular, gold nanoparticles have been intensively studied as they are versatile materials having interesting chemical, electronic and optical properties for a broad range of different applications. The properties and applications of gold nanoparticles strongly depend on their respective shape and size.
Possible applications of gold nanoparticles lie, for example, in the fields of nanoelectronics, imaging, sensing, catalysis, optics, environmental industry, energy development and biomedicine. Due to the low oxidation metal potential of gold nanoparticles, they can be used in medical diagnostic tests, such as labeling, X-ray contrasting, immunestrain and phago kinetic tracking studies, in targeted truck delivery techniques, as well as in medical therapies.
Silver nanoparticles have various and important applications. Historically, silver has been known to have a disinfecting effect and has been found in applications ranging from traditional medicines to culinary items. It has been reported that silver nanoparticles (AgNPs) are non-toxic to humans and most effective against bacteria, virus and other eukaryotic micro-organism at low concentrations and without any side effects. Moreover, several salts of silver and their derivatives are commercially manufactured as antimicrobial agents. In small concentrations, silver is safe for human cells, but lethal for microorganisms. Antimicrobial capability of AgNPs allows them to be suitably employed in numerous household products such as textiles, as well as disinfection in water treatment, food storage containers, home appliances and in medical devices. The most important application of silver and AgNPs is in medical industry such as tropical ointments to prevent infection against burns and open wounds.
Several methods for producing noble metal nanoparticles have been developed which utilize harsh conditions. Wet methods often require the application of aggressive reducing agents, for example sodium borohydride, capping agents and may additionally need organic solvents such as toluene or chloroform. Furthermore, often toxic compounds must be employed or are produced during the synthesis of noble nanoparticles. Although known methods may produce successfully noble metal nanoparticles, energy preparation consumption and pollution effects are relatively high, as well as materially and environmental costs. Even the availability of some materials, in particular of biomaterials, as for example plant materials, may be a problem. In consequence, there remains a need for more cost-effective and environmentally benign alternative methods for producing noble metal nanoparticles with improved properties on a large scale. Main criteria for a green chemistry synthesis of stabilized nanoparticles are the choice of eco-friendly and non-hazardous solvents, reducing agents and capping agents, especially for noble metal nanoparticles which shall be utilized in medical treatment.
Biological synthesis of nanoparticles by plant extracts is at present under exploitation as some researchers worked on it and tested then for antimicrobial activities.
Chemical reduction methods are widely used for synthesizing Ag—NPs because of their readiness to generate Ag—NPs under gentle conditions and their ability to synthesize Ag—NPs on a large scale.
US 2010/0055199 A1 discloses systems and methods for synthesizing silver nanoparticles using Trichoderma funghi. In an aspect, Trichoderma reesei was used for extracellular synthesis of silver nanoparticles. In the biosynthesis of metal nanoparticles by a fungus, one or more enzymes or metabolites are produced that reduce the silver ions to its metallic solid nanoparticles through a catalytic process.
US 2010/0200501 A1 relates to methods of making and using as well as compositions of metal nanoparticles formed by green chemistry synthetic techniques. The production of metal nanoparticles of Ag, Au, Pt, Pd, Fe, Mn, Cu and In in a single pot method using plant extracts as coffee and/or tee extract and use of these metal nanoparticles in removing contaminates from soil, groundwater and other contaminated sites are described. The reducing agent used for the preparation of the metal nanoparticles can be among others a phenolic compound or a flavonoid or a combination thereof.
For the last two decades extensive work has been done to develop new drugs from natural products because of the resistance of micro-organisms to the existing drugs. Nature has been an important source of products currently being used in medical practice.
There are various strategies for using gold nanoparticles as a drug delivery vehicle, including systems based on covalent binding or drug encapsulation. Furthermore, it has been reported that antibiotics often disturb the bacterial flora of digestive tract which may develop multiple drug-resistant isolates, hence novel ways of formulating biocide materials is an upcoming field of attraction. For this reason, there is a need for the use of an agent which does not generate resistance and presents a good bactericidal property. Gold nanoparticles have a great bactericidal effect on several ranges of microorganisms.
A number of synthetic methods have been employed for the synthesis of silver-based nanoparticles involving physical, chemical and biochemical techniques. However, these chemical synthesis methods employ toxic chemicals in the synthesis route which may have adverse effect in the medical applications and hazard to environment.